Herons: Info + Conservation

Great Blue Heron (Ardea herodius) is the largest and most widely distributed heron in Canada. During the breeding and post-breeding seasons it ventures as far north as Newfoundland and Prince William Sound in Alaska, and as far south as Mexico and the West Indies. Herons leave most of Canada for the winter, the exception being the British Columbia coast, where herons reside all year round. They also winter across the United States and south to Panama, Colombia, and Venezuela.

Two subspecies occur in BC : the coastal fannini ssp and the interior herodias ssp.

Elevation: 0-1100 m. The fannini subspecies of Great Blue Heron is found throughout the Coast Region. While foraging and breeding sites are quite dispersed, this subspecies is more common on the South Coast especially in association with low elevation lakes, wetlands, sloughs and estuaries. The major nesting colonies (“heronries”) on the South Coast include: Tsawwassen, Bowen Island, Deer Lake, UBC (main campus) and West Vancouver. Many of these locations support >100 nesting pairs. Other heronries occur on the Southern Gulf Islands and southeast Vancouver Island. A major heronry located at the confluence of the Coquitlam and Fraser Rivers adjacent to Colony Farm Regional Park became abandoned around 2012. Although some nesting may still be occurring there. It is estimated that approximately 4-5000 breeding birds make up the coastal subspecies population in BC, with some heronries like Tsawwassen supporting at least 10% of that population.

DISTINCTIVE FEATURES

On the ground, adult specimens stand over 1 metre in height. the head is white with a black stripe on each side extending back from the yellow eyes to slender black plumes. The back is greyish blue and the breast is white streaked with black. In flight, the neck is doubled back and the head rests against the shoulders. Herons in their first year have grey crowns and grey wing flecked with brown.

HABITAT

Habitat (especially during breeding season) includes riparian areas, estuaries, lakes and lowland rivers and streams. Foraging habitat includes: Eel grass beds, mudflats, agricultural fields and old-field (mainly short-grass or mowed), wharves, beaches, irrigation ditches, urban lakes, streams, drainage ditches and backyard ponds. During non-breeding periods birds roost high up in mature trees in close proximity to foraging sites. Heronries are typically found within 10 km of foraging habitats. Though generally associated with stands of trees well away from noise, light and human disturbance, some heronries (e.g. Stanley Park), have become established in dense urban areas. Canopy closure is a factor for heronries, typically being >80%, though birds have been known to use stands with more open canopies. Heronries can be over 350 nests and sites are reused in successive years. Small nesting colonies are more common on the Sunshine Coast and on Vancouver Island. Nests are located at 4-70 m above ground and consist of large stick platforms, < 1 m diameter. Nests are constructed on the horizontal branches of mature trees, often Black Cottonwood, Bigleaf Maple or conifers. Nests are lined with twigs; bark strips, coniferous boughs and rushes. Both the nest and the ground beneath are often covered in droppings, discarded food, and occasionally dead chicks.

DIET

Primarily a fish eater (pisciverous), this subspecies also exploits a range of amphibians including invasive species such as Green Frog and American Bullfrog. Small mammals such as Townsend’s Vole, mice and shrews are stalked in meadows and agricultural fields and may form an important component of the diet in winter in certain areas.

Check out these websites for more information on the Great Blue Heron:

Although the Great Blue Heron is commonly seen in parts of B.C., its numbers are decreasing. The main reason is human activity. Most of B.C.’s human population lives in the heron’s favourite areas – the coast and the southern interior. This makes it hard for herons to find undisturbed sites for nesting. The presence of humans as far away as 200 metres from a colony can cause the birds to abandon it. Sometimes, however, they become used to people. Herons have been nesting in Vancouver’s busy Stanley Park for over 75 years.

Because of the Great Blue Heron’s sensitivity to human activity and its declining population, it has been placed on B.C.’s Blue List of vulnerable species. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has designated the Pacific Great Blue Heron as Vulnerable.

THREATS

Habitat loss due to significant urbanization, draining and infilling of wetlands, foreshore development, logging and removal of riparian forest

Low breeding success and high rates of nest abandonment in response to disturbance and human activities. Canopy removal or clearing near a nesting area can cause nest abandonment and chick mortality

Increased predation by recovering bald eagle populations may result in low breeding success and abandonment of some nesting colonies